This invention relates to a corpuscular radiation device for producing an irradiation pattern on a workpiece by means of a beam produced by a first corpuscular radiation source, including a system for precisely recognizing the position of the workpiece as well as possibly for the adjustment thereof, both by means of irradiating the bottom major surface of the workpiece and of adjustment marks possibly applied there, by a beam produced by a second corpuscular radiation source, as well as means for determining the mutual positions of both beams relative to one another, for determining the position of the first beam relative to the workpiece and for recognizing and operatively monitoring the configuration of said beam originating from the first radiation source and producing the irradiation pattern.
Such a corpuscular radiation device is preferably suited for producing irradiation patterns on semiconductor wafers in the production of integrated circuits. In this context, it is known from numerous publications to print the pattern on the workpiece by a focussed electron beam which scans the regions to be irradiated.
Such methods have been discussed for instance in a paper by T. H. P. Chang, M. Hatzakis, A. D. Wilson, A. J. Speth, A. Kern: "Grundlagen and Technik der Elektronenstrahl-Lithographie"--Fundamentals and Engineering of electron beam lithography--(Elektronik 26 (1977) No. 8, pages 51-60). Furthermore, other methods are known wherein the irradiation pattern is produced across large areas by means of transradiation of accordingly shaped masks. In one of these methods which has been disclosed in the German Pat. No. 25 15 549 a mask electron-beam transparent in its free areas is reproduced on a reduced scale by means of electron-optical lenses. In another such method which has been reported on at the 42nd Physicists Conference 1978 in Berlin (Conference Magazine page 1210, lecture D 12.4) by H. Bohlen, J. Greschner, W. Kulcke and P. Nehmiz under the title "Elektronenstrahl-Lithographie mittels Schattenwurf einer Maske in Chip-Grosse"--Electron Beam Lithography by means of Shadow Projection of a Mask in Chip Size--a mask provided close to the workpiece surface and transparent to electrons in parts of its area according to the required pattern is projected by means of parallel electron irradiation as a shadow image upon the workpiece surface in a manner almost corresponding to a photographic contact copy process. Finally, a photo cathode has also been formed as a mask as presented for instance in the U.S. Pat. No. 3,895,234, and the electrons emitted upon light irradiation in the desired area distribution are guided on the workpiece surface by means of a homogenous magnetic field.
In a similar manner, exposure patterns may be plotted on the workpiece also with ion beams. So for instance G. Stengl has reported on an "Ion-Projection System for IC Production" at the 15th Symposium on Electron, Ion and Photon Beam Technology in Boston, Ma., U.S.A., 5-29 to 6-1-1979 (lecture G-1), and at the same Symposium, D. B. Rensch, R. L. Seliger and G. Csanky have reported on scanning ion beam methods unter the title "Ion-Beam Lithography for IC Fabrication with Submicrometer Features" (lecture G-5).
Frequently, a plurality of irradiation patterns must be produced on the workpiece one after the other. This is even the rule for the production of integrated semiconductor circuits, the workpiece being removed after effected exposure of a pattern from the corpuscular radiation device and being treated further in the required manner. Such well-known further treatment processes are for instance etching, vapor deposition and oxidizing of the workpiece surface or implanting ions and finally also the application of a layer sensitive to corpuscular radiation exposure which may be developed after a renewed exposition of a pattern selectively on irradiated or on non-irradiated surface regions by a chemical solution.
When plotting a further pattern on a semiconductor workpiece, the essential matter now is that the pattern assumes an accurately defined position in all its details in relationship to the structures already present on the workpiece, these having been produced for instance by means of one or more preceding exposures. There is the difficulty that the patterns to be exposed with the corpuscular beam predominantly consist of structures having very fine details within which the characteristic detail dimensions are around 1 .mu.m or even below and that therefore such fine structures are able to be superimposed satisfactorily in consecutive processing steps and brought into a correct functional interdependency only if their mutual position deviation remains small in relationship to the minimum dimensions of the structure details. This means, however, that the permissible mutual position insecurity between the finest structures of different processing operations may at the most be small fractions of a .mu.m.
Now the electron beam, however, is able to be deflected reasonably error-free along a distance of several mms only and since on the other hand in technology of producing integrated circuits the typical workpiece is a silicon wafer of a diameter of several cms, a mechanical transverse shifting of the silicon wafer must be coupled with a magnetic or electric deflection of the corpuscular beam if a pattern is to be exposed across the entire surface of the workpiece at disposal. For doing so, it is conventional to control the precision of the mechanical shifting motion of the table on which the workpiece is placed by means of a laser interferometer, as for instance described in a paper by H. de Lang and G. Bouwhuis: "Genaue digitale Messung von Verschiebungen mit optischen Mitteln II. Die Messung von Verschiebungen mit einem Laser-Interferometer"--Precise digital measurement of small mechanical translations employing optical means II. The measurement of small mechanical translations employing a Laser interferometer--(Philips techn. Rdsch. 30 (1969/70) No. 6/7, pages 165-170). With a laser interferometer, the position of the translation table may be monitored to about one quarter of the wavelength of the light used, i.e. to 0.1 to 0.2 .mu.m. This, however, still in no way means that the position of the point of impingement of the corpuscular beam upon the workpiece is known with the same precision. Rather, it has to be expected that the workpiece does not return to exactly the same position on the translation table when it has been removed between two pattern exposures for performing other processing steps from the corpuscular radiation device. Also, a shape variation of the workpiece may arise, for instance by distortion of the semiconductor wafer in the thermal processing steps in the course of producing highly integrated circuits.
In addition thereto, the point of impingement of the corpuscular beam may also be shifted in the workpiece plane in that the corpuscular-optical system of the irradiation device distorts in the event of minor fluctuations of temperature or by an internal temperature compensation or that a mechanical creeping occurs. Similar beam shifts may in addition thereto be caused by slow variations of the chargings at the internal wall of the corpuscular radiation device and the concurrent variation of beam repulsing, such variations of charging up often occurring with corresponding variations of the beam current.
Thus, a fine adjustment of the corpuscular beam is required in relationship to the workpiece surface. It is normal to direct the corpuscular beam to adjustment marks which have previously been applied to the surface of the workpiece. The adjustment marks and the environment thereof are then scanned in the form of line scans, and from the variation of the current of backscattered corpuscles or secondary emission electrons, the position of the edges of the adjustment marks is determined. Such adjustment marks are frequently arranged in such positions and in just so large a mutual spacing that they mark the corners of such a partial field of the surface with the workpiece stationary and thus solely by beam deflection can be scanned without any appreciable deflection error by the exposure pattern producing corpuscular beam. In numerous publications, there have been reports in literature on the shape and on the optimization of such adjustment marks at considering diverse aspects.
With these marks, a main disadvantage is that a part of the surface of the semiconductor wafer cannot be used for integrated circuits, namely that part of the surface which is covered by the adjustment marks themselves and the direct environment thereof which are scanned by the corpuscular beam when monitoring the position of the adjustment marks.
Other disadvantages result from a deterioration of the resolving power effective for localizing the mark positions: Obviously, during application of the lacquer coating, the adjustment marks are covered by the irradiation-sensitive lacquer coating as well as the far larger useful area actually to be described with the details of the integrated circuit. When the position of the adjustment marks is scanned with the corpuscular beam, the incident corpuscles must initially penetrate the lacquer coating before striking the adjustment marks for producing backscattered corpuscles and secondary emission electrons. When passing through the lacquer, the corpuscles are scattered, and there is an appreciable loss of resolving power in comparison to the accuracy attained in determining the position of adjustment marks not covered by lacquer.
Finally, in the known methods the location of the position of the adjustment marks requires time which is lost for the actual scanning processing of the workpiece, and a continuous control and monitoring of the workpiece position is principly not possible in real time.
In efforts to plot finer and finer structures with dimensions of clearly below 1 .mu.m the last mentioned restrictions become increasingly notable in particular.